The present invention relates to a mobile satellite communication terminal in a multi-beam satellite communication system, and more particularly to a beam automatic selection switching method for automatically selecting a beam used in the mobile satellite communication terminal as well as to an apparatus for the same.
There has been known a technology disclosed in Japanese Patent Laid-Open Publication No. 75518/1993 as a beam automatic selection switching method in a multi-beam satellite communication system. This beam automatic selection switching method, as shown in FIG. 6, comprises a line quality assessing means 100 for assessing a line quality of a signal received from the communication satellite in the mobile satellite communication terminal; a position computing means 101 for computing a current position of the mobile satellite communication terminal according to data received from a GPS; a moving direction detecting means 102 for detecting a moving direction (progressing direction) of the mobile satellite communication terminal by using an earth magnetic sensor or the like; a next beam computing means 103 for computing a beam to be selected next according to a current position of the mobile satellite communication terminal computed by the position computing means 101 as well as to a moving direction of the mobile satellite communication terminal detected by the moving direction detecting means 102; and a beam switching means 104 for transmitting a beam switching request command via the communication satellite to the earth station for switching the beam.
In this beam automatic selection switching method, when the assessment value of a line quality of the mobile satellite communication terminal is determined as worse than a prespecified threshold value by the line quality assessing means 100, at first the position computing means 101 computes a current position of the mobile satellite communication terminal. Then, a beam to be selected next is computed by the next beam computing means 103 according to the moving direction of the mobile satellite communication terminal detected by the moving direction detecting means 102 as well as the current position of the mobile satellite communication terminal computed by the position computing means 101 for deciding the beam, and the beam switching means 104 transmits a beam switching request command to the communication satellite.
Configuration of the beam switching apparatus based on the conventional technology is as described above, so that a long period of time is required for switching a beam, and communications may be cut during the processing described above, and for this reason it is quite inconvenient to use the apparatus.
It is an object of the present invention to obtain a beam automatic selection switching method in a multi-beam satellite communication system in which an easy-to-use mobile satellite communication terminal can be obtained by reducing a time required for switching beams as well as to obtain an apparatus for the same.
In the beam automatic selection switching method according to the present invention, a beam to be used can be selected by referring to the position-beam correspondence data table previously stored at some point of time when the mobile satellite communication terminal is not executing communications.
In the beam automatic selection switching method according to the present invention, a moving direction-beam correspondence data table is generated by the moving direction-beam correspondence data table generating means at an appropriate point of time when the mobile satellite communication terminal is not executing communications, and a next beam is selected with reference to the moving direction-beam correspondence data table when an assessment value for a line quality becomes worse, so that a beam can be switched within a short period of time even during communications while the communication terminal is moving.
In the beam automatic selection switching method according to the present invention, a beam to be used can be selected by referring to the position-beam correspondence data table previously stored at an appropriate point of time when the mobile satellite communication terminal is not executing communications, so that the beam can successively be corrected to an accurate beam, and a moving direction-beam correspondence data table is generated by the moving direction-beam correspondence data table generating means at some point of time when the mobile satellite communication terminal is not executing communications, and a next beam is selected with reference to the moving direction-beam data correspondence table when an assessment value for a line quality becomes worse, and for this reason a beam can be switched within a short period of time even during communications while the communication terminal is moving.
In the beam automatic selection switching method according to the present invention, data for the moving direction-beam correspondence data table is generated in the earth station, and this data is written via the communication satellite into the moving direction-beam correspondence data table therefrom.
In the beam automatic selection switching apparatus according to the present invention, a beam to be used is selected by referring to the position-beam correspondence data table previously stored at an appropriate point of time when the mobile satellite communication terminal is not executing communications.
In the beam automatic selection switching apparatus according to the present invention, a moving direction-beam correspondence data table is generated by the moving direction-beam correspondence data table generating means at an appropriate point of time when the mobile satellite communication terminal is not executing communications, and a next beam is selected with reference to the moving direction-beam correspondence data table when the assessment value for a line quality becomes worse. With this feature a beam can be switched within a short period of time even during communications while the communication terminal is moving.
In the beam automatic selection switching apparatus according to the present invention, a beam to be used is selected by referring to the position-beam correspondence data table previously stored at an appropriate point of time when the mobile satellite communication terminal is not executing communications; a moving direction-beam correspondence data table is generated by the moving direction-beam correspondence data table generating means at an appropriate point of time when the mobile satellite communication terminal is not executing communications, and a next beam is selected with reference to the moving direction-beam correspondence data table when the assessment value for a line quality becomes worse. With this feature, a beam can be switched within a short period of time even during communications while the communication terminal is moving.
In the beam automatic selection switching apparatus according to the present invention, a moving direction of the mobile satellite communication terminal can accurately be detected by a special purpose device such as an earth magnetic sensor or a gyroscope.
In the beam automatic selection switching apparatus according to the present invention, a moving direction of the mobile satellite communication terminal can be detected from position data for two points obtained by the position computing means without requiring a dedicated device.
In the beam automatic selection switching apparatus according to the present invention, a line quality of a signal received from the satellite can be assessed according to a bit error rate or a receiving level, or a C/N ratio.
Other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.